Electronic oven



y 3, 1967 F. A. REKER 3,321,605

ELECTRONIC OVEN Filed Aug. 6, 19 64 2 Sheets-Sheet 1 0- FIG.!

INVENTOR FREDR/CK A. REKER BY 67 k W ATTYS,

May 23, 1967 Filed Aug. 1964 2 Sheets-Sheet 2 FIG.3

IN VEN TOR I a 1 lII a a i 5 Y 2 O 5 7/8\ 0 O 7 7 8 M a A 33x3 k v FREDR/CK R R 252 BY A EKE J ATTYS.

United States Patent 3,321,605 ELECTRONIC OVEN Frederick A. Reker, Scarsdale, N.Y., assignor to General Electric Company, a corporation of New York Filed Aug. 6, 1964, Ser. No. 387,861 8 Claims. (Cl. 219-1055) The present invention relates to electronic ovens, and more particularly to such ovens incorporating therein ultra-high frequency electromagnetic wave energy transmission lines.

It is a general object of the invention to provide an improved electronic oven incorporating therein a transmission line of the type including a tubular outer conductor and an enclosed inner conductor for transmitting ultrahigh frequency electromagnetic wave energy from a generator therefor to a cooking cavity in the interior of the oven.

Another object of the invention is to provide an electronic oven having an improved transmission line of the type set forth, wherein the transmission line includes a tubular outer conductor and an inner conductor disposed therein, the inner conductor including two longitudinally disposed sections electrically insulated from each other, one of the inner conductor sections including a tube and the other of the inner conductor sections including a probe extending into the tube, and a ring of low-loss dielectric material carried by the probe in surrounding relation therewith and spaced away from the inner end of the probe and toward the outer end of the tube by substantially a predetermined distance, whereby in the transmission of the electromagnetic wave energy between the inner conductor sections there is effected high attenuation of a corresponding predetermined harmonic and substantial attenuation of the higher harmonics of the fundamental operating frequency of the generator.

Yet another object of the invention is to provide an electronic oven having an improved transmission line of the type set forth, wherein the tube and the probe and the ring provide a filter for effecting high attenuation of the second harmonic and substantial attenuation of the higher harmonics of the fundamental operating frequency of the generator.

Still another object of the invention is to provide an electronic oven having an improved transmission line of the type set forth, wherein the tube and the probe and the ring provide a filter for effecting high attenuation of the fourth harmonic and substantial attenuation of the higher harmonics of the fundamental operating frequency of the generator.

Yet another object of the invention is to provide an electronic oven having an improved transmission line of the type set forth, wherein the transmission line includes a tubular outer conductor and an inner conductor disposed therein, the inner conductor including two longitudinally disposed sections electrically insulated from each other, one of the inner conductor sections including a tube and the other of the inner conductor sections including a probe extending into the tube, a first ring of low-loss dielectric material carried by the probe in surrounding relation therewith and spaced away from the inner end of the probe and toward the outer end of the tube by substantially a first predetermined distance, whereby in the transmission of the electromagnetic wave energy between the inner conductor sections there is effected high attenuation of a corresponding first predetermined harmonic and substantial attenuation of the higher harmonic of the fundamental operating frequency of the generator, and a second ring of low-loss dielectric material carried by the probe in surrounding relation therewith and spaced away from the inner end of the probe and toward the outer end of the tube by substantially a second predetermined distance, whereby in the transmission of the electromagnetic wave energy between the inner conductor sections there is effected high attenuation of a corresponding second predetermined harmonic and substantial attenuation of the higher harmonics of the fundamental operating frequency of the generator.

Yet another object of the invention is to provide an electronic oven having an improved transmission line of the type set forth, wherein the low-loss dielectric material therein consists essentially of a synthetic organic polymer having a softening point at a relatively high temperature, the preferred synthetic organic polymer being polytetrafluoroethylene.

A further object of the invention is to provide an electronic oven having an improved trans-mission line of the type set forth, wherein there is further provided a plurality of longitudinally spaced-apart conducting discs carried by the inner conductor and extending radially outwardly toward the outer conductor to provide a relatively low impedance between the conductors for harmonies of the fundamental operating frequency of the generator.

A still further object of the invention is to provide an electronic oven having an improved transmission line of the type set forth, wherein the outer conductor includes two sections arranged in telescopic relation with each other, and further comprising a sleeve of electrical insulating material arranged in intervening relation to the two outer conductor sections at the telescopic joint therebetween.

Further features of the invention pertain to the particular arrangement of the parts and elements of the electronic oven, whereby the above-outlined and additional operating features thereof are attained.

The invention both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which:

FIGURE 1 is a side view with certain parts broken away of an electronic oven embodying therein the present invention;

FIG. 2 is a fragmentary view in vertical section on an enlarged scale with certain parts broken away of the imforming a part of the electronic oven of the present invention;

FIG. 3 is a view on a reduced scale in horizontal section through the upper portion of the transmission line along the line 33 of FIG. 2;

FIG. 4 is a view on a reduced scale in tion along the line 44 of FIG. 2; and

FIG. 5 is a view on a reduced scale in vertical section through the horizontal transmission line along the line 5-5 of FIG. 2.

Referring to FIG. 1 of the drawings, the electronic oven 10 there illustrated, and embodying the features of the present invention if of the fundamental construction and arrangement of that disclosed and claimed in the copending application of Louis H. Fitzmayer, Ser. No. 135,582, filed Sept. 1, 1961, now Patent No. 3,172,987, granted Mar. 9, 1965. More particularly, the oven 10 comprises an oven chamber or cooking cavity 11 defined by electrically conductive walls, and particularly by a box-like metal liner 112 including a top wall 13, a bottom wall 14, a rear wall 15 and two side walls 16, the front opening of the liner 12 being closed by a metallic oven door 17. The door 17 is provided with a hinge 17a and a handle 17b, whereby the door 17 may be moved between an open position and a closed position, suitable interlocking and switching apparatus (not shown) being provided to insure that there is no electromagnetic wave horizontal secenergy present within the cooking cavity 11 when the door 17 is in its open position.

As illustrated in the drawings, the appliance is in fact a combination electric and electronic oven and includes a pair of spaced-apart electric heating units of the sheathed resistance conductor type mounted on the lower surface of the liner top wall 13 and generally designated by the numeral The heating units 20 are generally rectangular in form and extend substantially parallel to the oven door 17 and are spaced-apart from front to rear of the liner 11 so that electromagnetic wave energy can be injected into the cooking cavity therebetween. A lower electric heating unit of the sheated resistance conductor type is also provided and is mounted slightly above the bottom wall 14 of the liner 12 and is generally designated by the numeral 60.

Disposed above the bottom Wall 14 of the liner 12 and also above the bottom heating unit 60 is a cooking platform generally designated by the numeral and including a central hub 31 from which extend radially outwardly a plurality of metallic rod-like arms 32 which carry thereon a floor 33 of metallic open-work construction, the outer ends of the arms 32 and the periphery of the floor 33 carrying a generally circular upstanding metallic rim 34 thereon. Formed integral with the hub 31 and extending downwardly therefrom in an arbor 35 that fits into a bearing 36 mounted on the bottom wall 14 and including a drive connection 81 for the arbor 35 to a drive unit 80 mounted below the bottom wall 14, the drive unit 80 being preferably an electric motor. Food to be cooked is placed upon the cooking platform 30 and the platform 30 is in turn driven by means of the drive unit 80- and the drive connection 81 and the arbor 35 at a rate of six revolutions per minute, for example, to pass the food upon the platform 80 through the electromagnetic field within the cooking cavity 11 so that various portions of the food being cooked are subjected to different field intensities, thereby equalizing the cooking thereof.

In order to collect the drippings and juices that are generated and which may fall from the cooking platform 30, a drip tray generally designated by the numeral 40 is provided beneath the cooking platform 30 but above the electric heating unit 60 so as to protect the electric heating unit 60 from the drippings. The drip tray 40 is formed of metal and performs a further function of shielding the electric heating unit 60 from the electromagnetic wave energy by providing a protective choke for the wave energy throughout substantially the lower portion of the cooking cavity 11, whereby to prevent the formation of parasitic currents in the lower heating unit 60, thereby protecting the heating unit 60 and preventing loss of electromagnetic wave energy therein. Conveniently, the drip tray 40 is supported upon the usual embossment's 16a provided upon the side wall 16 of the liner 12.

Positioned below the upper cooking cavity 11 is an apparatus compartment 70 within which is disposed a generator in the form of a magnetron 90 which serves as a source of ultra-high frequency electromagnetic wave energy for the cooking cavity 11, the magnetron 90 being of conventional form and having, for example, an operating frequency of 925 megacycles. The electromagnetic wave energy from the magnetron 90 is transmitted to the cooking cavity 11 via a transmission line of the coaxial conductor type made in accordance with an embodying the principles of the present invention and including four sections 100, 200, 300 and 400 connected in series and communicating with the interior of the cooking cavity 11 through a distribution box 50. More specifically, the magnetron 90 is disposed beneath the cooking cavity 11 and toward the rear thereof and is provided with a lower vertically extending transmission line section 100 of circular configuration connecting at a right angle with the lower horizontal transmission line section 200 of rectangular configuration which extends below and to the rear of the rear wall 15 of the cooking cavity 11. The rear end of the transmission line section 200 is connected at a right angle to the lower end of an upper vertical transmission line section 300 of circular configuration which has the upper end thereof connected at a right angle to the rear end of an upper horizontal and forwardly extending transmission line section 400 of rectangular configuration having the front end thereof connected at right angle to the distribution box 50.

The magnetron is provided with a field coil housing 91 including a central cylindrical member providing a metallic tubular outer conductor 110 that is substantially circular in cross section and has disposed centrally thereof a metallic stud 150 connected to the output terminal of the magnetron 90 and spaced from the conductor 110 by insulators including an insulator 160, the stud 150 being substantially circular in cross section. The tubular outer conductor 110 and the enclosed inner conductor or stud 150 comprise the first section of the transmission line interconnecting the magnetron 90 and the distribution box 50. The second transmission line section 200 includes a metallic tubular outer conductor 210 which is substantially rectangular in cross section as may be best seen in FIGS. 2 and 5 of the drawings, and includes wider upper and lower side walls 211 and 212 joined by narrower side walls 213 and 214. The bottom side wall 212 has a circular opening therein to the periphery of which is connected the outer tubular conductor forming a part of the first transmission line section 100. An inner conductor 220 is provided in the second transmission line section 200, the conductor 220 having a substantially rectangular cross section and being of ribbon-like configuration as can best be seen in FIGS. 2 and 5 of the drawings, the inner conductor 220 being disposed centrally of the outer conductor 210 with the flat surfaces thereof substantially parallel to the side walls 211 and 212. The end of the inner conductor 220 adjacent to the magnetron 90 is mounted on the outer conductor 210' by means of a suitable insulating block 221 which is held in position on the upper wall thereof and which also mounts thereon a resilient metallic conductor or bullet 222 which releasably and grippingly engages the stud 150, As may be best seen in FIGS. 1 and 2 of the drawings, the transmission line 200 extends rearwardly from the magnetron 90 and the rear end there-of is closed by a metallic end cap 230 having an annular flange 231 therearound fitting into the interior of the outer conductor 210 and enclosing the rear end thereof, the end cap 230 being held in position by screws 232. The rear end of the conductor 220 terminates a short distance from the end cap 230 and is supported by an insulator block 235 held in position within the outer conductor 210 by means of a screw 236.

The lower end of the transmission line section 300 connects with the rear or right hand end of the transmission line section 200 as viewed in FIG. 1, the transmission line section 300 including an outer tubular conductor generally designated by the numeral 301 and an enclosed inner conductor generally designated by the numeral 320. The outer conductor 301 includes a first metallic conductor section 302 which is generally circular in cross ection and has the lower end thereof mounted upon and connected to the top wall 211 of the outer conductor 210 as at 303, the lower end of the conductor section 302 surrounding a circular opening 215 in the top wall 211. The conductor section 302 extends upwardly from the top wall 211 a substantial distance and has the outer surface thereof surrounded by a sleeve 305 formed of an electrically insulated material, the sleeve 305 extending upwardly beyond the upper end of the conductor section 302 and terminating at the lower end thereof at a point spaced a short distance from the side wall 211 of the outer conductor 210. The preferred material of construction of the insulating sleeve 305 is a synthetic organic polymer, and more particularly a polymer formed of polytetrafluoroethylene resin sold under the trademark Teflon. A second metallic conductor section 310', also substantially circular in cross section, is provided, the inner diameter of the conductor section 310 being slightly greater than the outer diameter of the conductor section 302 and substantially equal to the outer diameter of the insulating sleeve 365. Surrounding the insulating sleeve 3435 is a cylindrical metallic sleeve 315 which closely interfits with the insulating sleeve 335 and extends from a point adjacent to the lower end thereof upwardly and beyond the upper end thereof and into overlying relationship with the lower end of the metallic conductor section 319. The internal diameter of the metallic sleeve 315 is slightly greater than the external diameter of the conductor section 310' to provide lateral mechanical support therefor while holding the conductor section 310 in contact with the upper end of the insulating sleeve 305, whereby the conductor sections 302 and 310 are held in firm mechanical alignment but are electrically insulated from each other by means of the electrically insulating sleeve 305.

The inner conductor 320 includes two longitudinally disposed conductor sections 330 and 350 electrically insulated from each other. The lower conductor section 330 includes a generally cylindrical tube 331 which has an outer diameter substantially less than the inner diameter of the outer conductor section 302, the lower end of the tube 331 being closed by a plug 332 having an outwardly extending flange 333 thereon, the plug 332 being suitably secured to the lower end of the tube 331 such as by brazing, both the tube 331 and the plug 332 being formed of a good electrical conducting material, preferably copper. The plug 332 rests upon the upper surface of the inner conductor 220 supported by the insulating block 235, and a suitable fastener in the form of a screw 334 passes through the plug 332, the conductor 220 and into the insulating block 235 firmly to mount the tube 331 thereon and to provide a good electrical interconnection between the inner conductor 220 and the inner conductor section 330'.

Spaced along the inner conductor section 330 and extending radially outwardly therefrom are four discs, two of the discs having a lesser thickness and being designated by the numerals 341 and 342, and two f the discs having a greater thickness and being designated by the numerals 343 and 344. All of the discs 341, 342, 343 and 344 have a generally circular shape as is best seen in FIG. 4 and are disposed concentrically with respect to the inner surface of the outer conductor section 302 and completely surround the inner conductor section 330, the disc being suitably mounted in the desired position along the inner conductor 330 by brazing as at 345. The thinner discs 341 and 342 preferably have a predetermined thickness X as indicated in FIG. 2, the thicker discs 343 and 344 have a predetermined thickness Y, and the distance between the facing surface of adjacent discs is a predetermined value W. The discs 341, 342, 343

and 344 in cooperation with the outer conductor section 302 provide a relatively low impedance path between the conductor sections 302 and 330 for the harmonics of the fundamental operating frequency of the generator 30, whereby to bypass the major portion of those harmonies and prevent transmission thereof along the transmission line section 300 to the conductors 310 and 350.

The second inner conductor section 350 includes a metallic tube 351 having a substantially circular cross section. There is provided on the lower end of the tube 351 an enlargement 352 which is provided with slots 353 to facilitate insertion thereof into a cup 354 including a cylindrical upstanding wall 355 receiving the enlargernent 352 therein and having the lower end thereof closed by a transverse wall 356. The cup 354 carries therebe neath a probe 360 which is formed as a solid rod Otf a good electrical conducting material such as copper, the cross section of the probe 360 being substantially circu- '365 firmly to clamp the ring 370 lar as is best seen in FIG. 4. The probe 360 is more specifically mounted upon the cup 354 by means of a screw 357 extending through an opening in the bottom of the cup 354 and threadedly engaging a complementarily threaded opening in the upper end of the probe 360, the probe 360 being disposed substantially concentrically with respect to the upstanding wall 355 of the cup 354 and being disposed substantially concentrically with respect to the tube 330 within which it is disposed and into which it extends.

The upper end of the probe 360 is provided with an annular shoulder 361 extending therearound and receiving thereon a ring 370 of low loss dielectric material which is disposed in surrounding relationship with respect to the upper end of the probe 360 and particularly about the portion of the probe 360 disposed above the shoulder 361 thereon. The ring 370 further has an opening generally centrally thereof receiving therethrough the shank of the screw 357 and also has an outwardly extending flange 371 extending well beyond the outer surface of the upper end of the probe 360 and engaging and overlying and substantially closing the upper end of the tube 330. In order fixedly to mount the cup 354 upon the tube 330 and fixedly to position the ring 370 upon the upper end of the tube 330 in closing relationship with respect thereto, and in order firmly to position the probe 360 centrally with respect to the tube 330, a cap 365 is provided including an annular outer wall 366 surrounding the upper end of the tube 330 and an inturned flange 360 engaging the ring flange 371. The inner surface of the wall 366 is threaded as :at 368 and threadedly engages external threads 338 on the upper end of the tube 330, the cooperating threads 338 and 368 enabling the cap upon the upper end of the tube 330; more specifically the flange 367 on the cap 365 engages the flange 371 on the ring 370 and urges it downwardly against the upper end of the tube 330 to provide a firm and tight seal therearound.

The ring 370 serves as a good electrical insulator between the lower inner conductor section 330 and the upper inner conductor section 350, and more specifically, provides good electrical insulation between the tube 331 and the probe 360 disposed therein. In addition, the ring 370 serves to insulate the cup 354 from the cap 365, a predetermined capacitance being formed between the cup 354 and the cap 365 as will be described more fully hereinafter. Preferred materials of construction of the ring 370 are synthetic organic polymers, any such polymer having the requisite electrical insulating properties and the low-loss characteristics at the higher harmonies of the operating frequency of the generator being suitable, such as for example, polyethylene, polystyrene, polytetrafluoroethylene, and the like. Of particular utility are those synthetic organic polymers that have a softening point at a relatively high temperature since the metallic parts of the transmission line section 300 are heated by the operation of the electronic oven lift, a preferred example of a polymer having a softening point at a relatively high temperature being polytetrafluoro'ethylene which has a softening point above 550 F. A second ring 380 of low-loss dielectric material is carried by the probe 360 intermediate the ends thereof and in surrounding relationship therewith. There is provided in the probe 360 a diametrally oriented opening 363 disposed in the illustrative example approximately one-third of the length thereof away from the inner end 362, and the ring 380 has therein aligned openings 381 which are disposed in registration with the opening 363 in the probe 360. A body 382 of cement is disposed in the aligned openings 363 and 381 fixedly to secure the ring 381 longitudinally with respect to the probe 360. The preferred material of construction of the ring 380 is the same as that of the ring 370* described above, i.e., a synthetic organic polymer, and particularly such a polymer having a softening point at a relatively high temperature, the preferred material of construction being polytetrafiuoroethylene. The body 382 of cement must also be insulating in character and capable of withstanding the relatively high temperatures that may be encountered in the transmission line section 300.

During the operation of the transmission line section 300, the tube 331 and the probe 360 cooperate to provide a filter whereby substantially to prevent transmission of the second and higher harmonics of the fundamental operating frequency of the generator 90 along the transmission section 300, and specifically, from the lower inner conductor section 330 to the upper inner conductor section 350. By lengthening or shortening the probe 360, the attenuation of the higher harmonics of the generator 90 can be increased or decreased, and positioning the ring 380 at different points along the probe 360 serves to cause preferential attenuation of one frequency with respect to another frequency or other frequencies. In the from of the invention illustrated in the drawings, the filter formed by the tube 331 and the probe 360 is designed specifically to provide high attenuation of the second harmonic and fourth harmonic of the fundamental operating frequency of the generator 90, and to provide a desired balance of the attenuation between the second harmonic and the fourth harmonic of the fundamental operating frequency of the generator 90. To this end, the length of the probe 360 and the position of the ring 370 thereon, i.e., the distance between the ring 370 and the inner end 362 of the probe 360, is predetermined so that there is effected high attenuation of the second harmonic of the fundamental operating frequency of the generator 90, the distance between the ring 370 and the inner end 362 of the probe 360 in the illustrative example being equal substantially to three-eighths wave length of the second harmonic of the fundamental operating frequency of the generator 90. The position of the ring 380 from the outer end 362 of the probe 360 is also predetermined and is selected so that there is effected a high attenuation of the fourth harmonic of the fundamental operating frequency of the generator, the predetermined distance being equal substantially to a quarter wave length of the fourth harmonic of the fundamental operating frequency of the generator 90. When the parts are so arranged and related with respect to each other, a maximum attenuation of the second and fourth harmonics is achieved, and there further is provided high attenuation of the higher harmonics of the fundamental operating frequency of the generator 90. The ring 370 being of a low-loss dielectric material and positioned as indicated provides a high-loss or attenuation of the fourth harmonic, whereby to achieve a balanced maximum attenuation of the second and fourth harmonics and higher harmonics of the fundamental operating frequency of the generator 90.

In the operation of the filter including the tube 331, the cup 354,.the probe 360 and the cap 365 a predetermined capacitance is provided between the tube 331 and the probe 360, and particularly between the cap 365 closing the upper end of the tube 331 and the cup 354 at the upper end of the probe 360. The length of the probe 360 is chosen so that the inductance thereof at the second and fourth harmonics of the fundamental operating frequency of the generator 90 resonates with the capacitance between the cup 354 and the cap 365 and the other capacitance between the tube 331 and the probe 360. The higher the capacitance between these parts, the lower the resonant frequency of the filter formed thereby, and vice versa, the lower the capacitance between these parts the higher the resonant frequency of the filter formed thereby. The ring 380 serves as a transformer and is positioned along the probe 360 a proper distance from the end 362 thereof so that the filter formed by the various parts named will filter both the second and fourth harmonics of the fundamentel operating frequency of the generator 90. If the tranformer provided by the ring 380 is not properly located along the length of the probe 360, a maximum rejection will not occur at two frequencies that are multiples of each other, i.e., there will not be maximum rejection at the second and fourth harmonics of the fundamental operating frequency; on the other hand, proper positioning of the transformer represented by the ring 380 will provide for maximum rejection of the second and fourth harmonics. The attenuation of the second and fourth harmonics is fundamentally obtained because the inductance provided by the probe 360 resonates with the capacitance between the probe 360 including the connected parts thereof such as the cup 354 and the tube 331 including the connected parts thereof such as the cap 365 at the second and fourth harmonics. The tube 331, the probe 360 and the ring 380 together with the attached parts provide a filter which can be considered to be essentially a parallel resonant circuit in series with the inner conductor 320 of the transmission line section 360, and more particularly a parallel resonant circuit in series between the inner conductor section 330 and the inner conductor section 356.

The provision of the insulating sleeve 305 between the outer conductor sections 302 and 310, and the provision of the insulating ring 370 between the inner conductor section 330 and the inner conductor section 350 further provides insulation between the respective conductor sections so that there is no D.C. connection therebetween, whereby the relatively high D.C. potentials on the outer conductor'Zltl are not applied to the outer conductor section 310, and likewise any D.C. potentials on the inner conductor 220 are not applied to the inner conductor section 350, and in fact the outer conductor section 310 or the inner conductor section 350 can be grounded if desired, the outer conductor section 310 in fact being grounded as will be described more fully hereinafter. In addition, the parts thus described, including the lower end of the outer conductor section 310 cooperating with the outer metallic sleeve 315 and the lower end 352 of the inner conductor section 350 cooperating with the cup 354, provide a readily separable connection which facilitates assembly and diassembly of the upper transmission line sections 310-354) with respect to the lower transmission line sections 302-330.

The upper end of the transmission section 300 is connected at a right angle to the rear end of the transmission line section 400. Referring to FIG. 1 of the drawings, it will be seen that the transmission line section 400 is provided with a metallic tubular outer conductor 410 which has a substantially rectangular cross section. Disposed within the outer conductor 410 and enclosed thereby is a metallic inner conductor 450 which also is rectangular in cross section and is disposed substantially centrally of the outer conductor 410. The end of the outer conductor 410 disposed adjacent to the upper end of the transmission line section 300 is closed by an end cap 420 which is adapted to fit within the outer conductor 410, the end cap 420 substantially filling and closing the outer conductor 410 and being held in position thereon by fasteners, not shown. The adjacent end of the inner conductor 450 is supported within the outer conductor 410 on an insulating block 440 which is held in position upon the conductor 410 and which carries a metallic connector 443 in electrical connection with the electrical conductor 450 and which receives and forms an electrical connection with the upper end of the inner conductor section 350, the inner conductor section 350 extending upwardly through a circular opening in the lower side of the outer conductor 410. The upper end of the outer conductor section 310 surrounds the circular opening in the lower wall of the outer conductor 410 and is held in proper relationship therewith by means of a fitting 431 mounted on the lower wall of the outer conductor 410.

The other or front end of the transmission line section 50 is connected to the distribution box 50, the outer conductor 410 abutting and being joined to the adjacent wall of the distribution box 50 and surrounding an opening therein through which extends the adjacent end of the inner conductor 450. More specifically, the adjacent end of the inner conductor 450 is mounted upon an insulating block 470 supported by the lower wall of the outer conductor 410 and further extends into the distribution box 50 and thus beyond the forward end of the outer conductor 410. The inner conductor 450 is bent downwardly as at 451 and terminates in an outwardly extending probe 452 disposed below the parallel to the main body on the inner conductor 450.

The distribution box 50 is formed of metal and is substantially closed around the four vertical sides of the top thereof, the bottom of the distribution box 50 being closed by a pane 71 of material which is impervious to oven gases but which is highly transparent to electromagnetic Wave energy, a preferred material of construction being a fused mixture of powdered glass and mica sold under the trademark Mykroy. The pane 71 also is in registration with a window formed on the top wall 13 of the liner 12 so that the electromagnetic wave energy delivered to the distribution box 50 can be directed through the pane 71 and into the interior of the cooking cavity 11.

There further is provided in the distribution box 50 a metallic tuning rod 75 which extends into the distribution box 50 and overlies the probe 452, the position of the tuning rod 75 being adjustable so as to obtain the desired tuning action.

In a preferred constructional example of the electronic oven 10, the magnetron 90 is designed and operated to produce a fundamental frequency of about 925 megacycles, whereby the fundamental frequency has a Wave length of about 12.77 inches. In such a construction, it is desired highly to attenuate the second harmonic of 1850 megacycles and the fourth harmonic of 3700 megacycles by means of the filter provided by the tube 331 and the probe 360. To achieve the maximum attenuation of the second and fourth harmonics, and further to achieve a balanced attenuation thereof, the parts have the following illustrative dimensions and ranges of dimensionsz The tube 331 has an overall length in the range 3.48 to 3.49 inches, an internal diameter in the range 0.539 to 0.543 inch and an external diameter of 0.625 inch; the probe 360 has a length measured between the shoulder 361 and the inner end 362 in the range 2.58 to 2.59 inches, a diameter in the range 0.311 to 0.314 inch and a distance in the range 0.99 to 1.00 inch from the center of the opening 363 to the inner end 362 thereof; the ring 380 has an outer diameter in the range 0.425 to 0.435 inch, and a longitudinal extent in the range 0.245 to 0.255 inch; and the distance Z, i.e., the distance between the lower edge of the ring 380 and the inner end 362 of the probe 360 is in the range 0.86 to 0.88 inch. In such an oven construction, the discs 341, 342, 343 and 344 have a diameter in the range 1.31 to 1.32 inches; the discs 341 and 342 have a thickness X in the range 0.122 to 0.128 inch; the discs 343 and 344 have a thickness Y in the range 0.193 to 0.199 inch; and the distance W between the facing surfaces of adjacent discs is 0.625 inch.

From the above it will be seen that there has been provided an improved electronic oven incorporating therein a transmission line of the type including a tubular outer conductor and an enclosed inner conductor for transmitting ultra-high frequency electromagnetic wave energy from a generator therefor to a cooking cavity in the interior of the oven, the inner conductor including two longitudinally disposed sections electrically insulated from each other, one of the inner conductor sections including a tube and the other of the inner conductor sections including a probe extending into the tube, and a ring of low-loss dielectric material carried by the probe in surrounding relation therewith and spaced away from the inner end of the probe and toward the outer end of the tube by substantially a predetermined distance, whereby in the transmission of electromagnetic wave energy between the inner conductor sections there is effected high attenuation of the higher harmonics of the fundamental operating frequency of the generator. There further has been provided a second ring of low-loss dielectric material carried by the probe in surrounding relation therewith and spaced from the inner end of the probe and toward the outer end of the tube by substantially a second predetermined distance whereby in the transmission of the electromagnetic wave energy between the inner conductor sections there is effected high attenuation of a corresponding other predetermined harmonic and substantial attenuation of the higher harmonics of the fundamental operating frequency of the generator. Further the attenuations of the second and higher harmonics of the fundamental operating frequency of the generator and the attenuations of the fourth and higher harmonics of the fundamental and operating frequency of the generator are balanced to provide the desired attenuations thereof within the improved transmission line.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein and it is intended to cover in the appended claims all such modifications that fall within the true spirit and scope of the invention.

What is claimed is:

1. An electronic oven comprising structure defining an apparatus compartment and a cooking cavity, a generator disposed in said apparatus compartment for generating ultra-high frequency electromagentic wave energy, a transmission line of the coaxial conductor type interconnecting said generator and said cooking cavity, whereby the electromagnetic wave energy is supplied into said cooking cavity via said transmission line from said generator, said transmission line including a tubular outer conductor and an inner conductor disposed therein, said inner conductor including two longitudinally disposed sections electrically insulated from each other, one of said inner conductor sections including a tube and the other of said inner conductor sections including a probe extending into said tube, and a ring of low-loss dielectric material carried by said probe in surrounding relation therewith and spaced away from the inner end thereof by a predetermined distance equal substantially to a quarter wave length of the fourth harmonic of the fundamental operating frequency of said generator, whereby in the transmission of the electromagnetic wave energy between said inner conductor sections there is effected high attenuation of the fourth harmonic and substantial attenuation of the higher harmonics of the fundamental operating frequency of said generator.

2. An electronic oven comprising structure defining an apparatus compartment and a cooking cavity, a generator disposed in said apparatus compartment for generating ultra-high frequency electromagnetic wave energy, a transmission line of the coaxial conductor type interconnecting said generator and said cooking cavity, whereby the electromagnetic wave energy is supplied into said cooking cavity via said transmission line from said generator, said transmission line including a tubular outer conductor and an inner conductor disposed therein, said inner conductor including two longitudinally disposed sections electrically insulated from each other, one of said inner conductor sections comprising a tube and the other of said inner conductor sections including a probe extending into said tube, the capacitance between said inner conductor sections cooperating with the inductance presented by the length of said probe within said tube to provide in series in said inner conductor a parallel resonant circuit having a high impedance at a predetermined harmonic of the fundamental operating frequency of said generator highly to attenuate the predetermined harmonic, and a transformer ring of low-loss dielectric material carried by said probe in surrounding relation therewith and spaced from the inner end thereof a predetermined distance equal substantially to a quarter wave length of a frequency higher than the predetermined harmonic, whereby in the transmission of the electromagnetic wave energy between said inner conductor sections there is effected high attenuation of both the predetermined harmonic and the frequency higher than the predetermined harmonic and the yet higher harmonics of the fundamental operating frequency of said generator.

3. The electronic oven set forth in claim 2;, wherein said predetermined distance is equal substantially to a quarter wave length of the second harmonic of the predetermined harmonic, whereby in the transmission of the electromagnetic wave energy between said inner conductor sections there is effected high attenuation of both the predetermined harmonic and the second harmonic of the predetermined harmonic and the higher harmonics of the fundamental operating frequency of said-generator.

4. The electronic oven set forth in claim 2, wherein said capacitance and said inductance provide in series in said inner conductor a parallel resonant circuit having a high impedance at the second harmonic of the fundamental operating frequency of sald generator highly to attenuate the second harmonic, and said predetermined distance is equal substantially to a quarter wave length of the fourth harmonic of the fundamental operating frequency of said generator, whereby in the transmission of the electromagnetic wave energy between said inner conductor sections there is effected high attenuation of both the second harmonic and the fourth harmonic and higher harmonics of the fundamental operating frequency of said generator.

5. The electronic oven set forth in claim 2, and further comprising a plurality of longitudinally spaced-apart conductive discs carried by said inner conductor and extending radially outwardly toward said outer conductorv to provide a high impedance in series for the third and higher harmonics of the fundamental operating frequency and to provide'a relatively low impedance path between said inner and outer conductors for the third and higher harmonics of the fundamental operating frequency.

6. The electronic oven set forth in claim 2, wherein said outer conductor includes two sections arranged in telescopic relation with respect to each other at a point disposed between the juncture of said inner conductor sections and said cooking cavity, and further comprising a sleeve of electrically insulating material arranged in intervening relation to said two outer conductor sections at the telescopic joint therebetween.

7. An electronic oven comprising structure defining an apparatus compartment and a cooking cavity, a generator disposed in said apparatus compartment for generating ultra-high frequency electromagnetic wave energ a transmission line of the coaxial conductor type interconnecting said generator and said cooking cavity, whereby the electromagnetic wave energy is supplied into said cooking cavity via said transmission line from said generator, said transmission line including a tubular outer conductor and an inner conductor disposed therein, said inner conductor including two longitudinally disposed sections electrically insulated from each other, one of said inner conductor sections comprising a tube and the other of said inner conductor sections including a probe extending into said tube, a first ring of lOW-lOSs dielectric material carried by said probe in surrounding relation therewith and spaced away from the inner end thereof by substantially a first predetermined distance, the capacitance between said inner conductor sections cooperating with the inductance presented by the length of said probe within said tube and said first predetermined distance to provide in series in said inner conductor a parallel resonant circuit having a high impedance at the second harmonic of the fundamental operating frequency of said generator highly to attenuate the second harmonic, and a second ring of low-loss dielectric material carried by said probe in surrounding relation therewith and spaced from the inner end thereof by substantially a second predetermined distance equal substantially to a quarter wave length of the fourth harmonic of the fundamental operating frequency of said generator, whereby in the transmission of the electromagnetic wave energy between said inner conductor sections there is effected the maximum high attenuation of both the second harmonic and the fourth harmonic of the fundamental operating frequency of said generator and high attenuation of yet higher harmonics of the fundamental operating frequency of said generator.

8. The electronic oven set forth in claim 7, and further comprising four longitudinally spaced-apart conductive discs carried by said tube and extending radially outwardly toward said outer conductor to provide a high impedance to the transmission along said transmission line of the third and higher harmonics of said fundamental operating frequency and to provide a relatively low impedance path between said discs and said outer conductor for the third and higher harmonics of said fundamental operating frequency, whereby to prevent the transmission of the third and higher harmonics of said fundamental operating frequency to said cooking cavity.

References Cited by the Examiner UNITED STATES PATENTS 2,700,136 1/1955 Devot 33373 2,968,772 1/1961 Thomas 333-73 FOREIGN PATENTS 525,018 5/1956 Canada.

RICHARD M. WOOD, Primary Examiner.

L. H. BENDER, Assistant Examiner. 

1. AN ELECTRONIC OVEN COMPRISING STRUCTURE DEFINING AN APPARATUS COMPARTMENT AND A COOKING CAVITY, A GENERATOR DISPOSED IN SAID APPARATUS COMPARTMENT FOR GENERATING ULTRA-HIGH FREQUENCY ELECTROMAGNETIC WAVE ENERGY, A TRANSMISSION LINE OF THE COAXIAL CONDUCTOR TYPE INTERCONNECTING SAID GENERATOR AND SAID COOKING CAVITY, WHEREBY THE ELECTROMAGNETIC WAVE ENERGY IS SUPPLIED INTO SAID COOKING CAVITY VIA SAID TRANSMISSION LINE FROM SAID GENERATOR, SAID TRANSMISSION LINE INCLUDING A TUBULAR OUTER CONDUCTOR AND AN INNER CONDUCTOR DISPOSED THEREIN, SAID INNER CONDUCTOR INCLUDING TWO LONGITUDINALLY DISPOSED SECTIONS ELECTRICALLY INSULATED FROM EACH OTHER, ONE OF SAID INNER CONDUCTOR SECTIONS INCLUDING A TUBE AND THE OTHER OF SAID INNER CONDUCTOR SECTIONS INCLUDING A PROBE EXTENDING INTO SAID TUBE, AND A RING OF LOW-LOSS DIELECTRIC MATERIAL CARRIED BY SAID PROBE IN SURROUNDING RELATION THEREWITH AND SPACED AWAY FROM THE INNER END THEREOF BY A PREDETERMINED DISTANCE EQUAL SUBSTANTIALLY TO A QUARTER WAVE LENGTH OF THE FOURTH HARMONIC OF THE FUNDAMENTAL OPERATING FREQUENCY OF SAID GENERATOR, WHEREBY IN THE TRANSMISSION OF THE ELECTROMAGNETIC WAVE ENERGY BETWEEN SAID INNER CONDUCTOR SECTIONS THERE IS EFFECTED HIGH ATTENUATION OF THE FOURTH HARMONIC AND SUBSTANTIAL ATTENUATION OF THE HIGHER HARMONICS OF THE FUNDAMENTAL OPERATING FREQUENCY OF SAID GENERATOR. 